The researchers were looking into "game transfer phenomena" which includes "perceptions, cognitions and behaviours influenced by videogame playing," and about 12 percent of the 1244 people they surveyed admitted to actually hearing sound effects, music and characters as they were going about their lives. One provided anecdote mentions a voice yelling "go, go, go" when the person couldn't get past other people on the subway.

The key point here is these hallucinations usually happen after extremely long sessions—like a whole day, not just a couple hours—and the researchers say these may not be super worrisome.

"Game Transfer Phenomena appears to be commonplace among excessive gamers and most of these phenomena are short-lasting, temporary, and resolve of their own accord," researcher professor Mark Griffiths explained in the press release about the study, which has been published in the International Journal of Cyber Behaviour, Psychology and Learning (find it here).

Griffiths also called these occurrences "conditioned responses," which does make sense as the transfer phenomena isn't just sounds, but also reflexive actions or visual hallucinations (like seeing menu screens). Many of us can probably relate to this to some degree, especially if there's been one game you've binged on over weeks or months. There's one music cue in Star Wars: The Old Republic, which plays every time you enter the Republic Senate building, that I heard everywhere for a few weeks in 2012.

I'm curious about this. If you've got a relevant anecdote, I'd like to hear it.